Senate Majority Leader Harry Reid (D-Nev.), center, speaks at a news conference with, from left, Sens. Mark Udall (D-Colo.), Charles Schumer (D-N.Y.), Dick Durbin (D-Ill.) and Patty Murray (D-Wash.) on July 10. (© Joshua Roberts / Reuters/REUTERS)

Less than two months after their most joyous moment together, the relationship between the Obama White House and Senate Democrats went off track and has never recovered.

Instead of basking in the victory glow of President Obama’s impressive 2012 reelection and an improbable two-seat gain for Democrats, they found themselves at the edge of the now infamous “fiscal cliff.”

Washington was consumed by negotiations over a huge stockpile of expiring tax cuts and automatic spending cuts that were set to kick in at the end of the year. The two months between Election Day and New Year’s Eve were a period of intense, partisan negotiations.

Senate Majority Leader Harry M. Reid (D-Nev.) had pulled back from the talks, leaving the White House, in the person of Vice President Biden, to cut a deal with Senate Minority Leader Mitch McConnell (R-Ky.).

The final vote on the package seemed like a bipartisan triumph: 89 senators supported the deal, which included the permanent extension of the Bush-era tax breaks for most workers. But the vote masked a vast underlying tension among some of the players.

The Fix's Chris Cillizza looks at three of the Senate battles that threw even the biggest political wonks for a loop. Which Senate showdowns made the cut? (Julie Percha/The Washington Post)

The episode left a particularly bitter taste for Reid’s chief of staff, David Krone, who had been privately assuring people that there would be no deal and that Congress would go “over the cliff” — as taxes soared for every American, giving the Democrats great political leverage when Congress returned for a period of more intense negotiations in January 2013.

Technically, the president’s first term wasn’t even complete, and he had just been reelected, but the fault lines within his own party were already sharply drawn. That tension blew up Tuesday when Krone’s comments about Democrats’ dismal showing in the 2014 midterms went public. He accused Obama of paying “lip service” to concerns about helping finance the midterm elections and said the president was an anchor that took down Democrats across the country, costing them the Senate majority.

“The president’s approval rating is barely 40 percent,” Krone said. “What else more is there to say?”

It was an unusual breach of Washington decorum that stunned a political community used to the shadowy “background” comments from “senior administration officials” or “senior Senate aides.” In general, staffers do not say such things on the record about a sitting president, especially from the same party.

[READ: More about Krone’s comments and how Democratic infighting helped Republicans gain control of the Senate]

Krone’s move wasn’t some rogue operation of a staffer gone wild. He is a close and loyal aide to Reid, having met him years ago when he — Krone — was a telecommunications lobbyist and executive. He’s the rare senior congressional staffer who did the reverse move in the revolving door — he made his millions on the outside, including a stint with Comcast, and then went into the public sector to work for Reid.

Krone joined Reid’s team as deputy chief of staff, helping guide him through a rocky 2010 reelection, and for the past four years as chief, Krone has channelled Reid. So his comments can reasonably be viewed as Reid’s views of Obama.

The majority leader and the president have had an odd relationship.

In the first two years of Obama’s presidency, Reid and Senate Democrats were the bulwark of Obama’s agenda. Then-Speaker Nancy Pelosi’s massive House majority could afford to lose the support of up to 40 members and still pass the president’s policies under the chamber’s simple majority rules, but Reid had to corral all 60 members of the Democratic caucus to pass legislation that wasn’t necessarily in the best interest of some senators from deeply conservative states.

Consistently, Senate Democrats felt that they were taking on the most risk as they supported Obama’s $800 billion stimulus plan, the Dodd-Frank rewrite of Wall Street laws and, most of all, the Affordable Care Act. These included a group of senators who first won seats in 2008 and rode into office with Obama. Among them were Mark Begich (Alaska), Kay Hagan (N.C.), Jeanne Shaheen (N.H.), Mark Udall (Colo.) and Mark Warner (Va.).

Three of those five appear to have lost on Tuesday, and Shaheen and Warner survived only by the narrowest of margins.

Throughout the tough votes, those Democrats enjoyed almost no real relationship with Obama, whose approach to social engagement with lawmakers is almost nonexistent.

Udall is considered one of the best golfers in the Capitol, and also one of the most genuinely likable people. In six years, he was asked to join the president for a round of golf just once — a few days after The Washington Post noted that Obama had never played golf with Udall. (The round was on a Monday afternoon, and it lasted only 15 holes because the Senate came back into session and votes were called.)

The Obama-Senate Democrats relationship somehow remained intact even through the tough 2010 midterm elections, when Democrats lost the House majority and saw their Senate count shrink to 53 seats.

In the summer of 2011, Obama played a round of golf with House Speaker John A. Boehner (R-Ohio). From there, the duo got close to reaching a massive budget deal that would have raised taxes and cut entitlement programs — slashing at two political sacred cows for Republicans and Democrats.

But Reid’s operation, along with his close ally, Sen. Charles E. Schumer (D-N.Y.), did not trust Obama’s negotiating skills, and at one point they directly leaked the emerging proposal, timing the release precisely so that the news broke just as Jack Lew, then the director of the Office of Management and Budget, entered a meeting with Senate Democrats.

As aides then recounted, Reid read the news bulletin aloud to a stunned audience of staunch liberals who had protected Social Security and Medicare with their political lives. Reid turned the lectern over to Lew.

The grand bargain, at that point, was essentially dead.

In 2012, however, the two sides ran perfect campaigns.

Then came “the cliff.”

Boehner and Obama again came close to a grand bargain, and it infuriated Democrats who saw it as fruitless, given how slight a hold the speaker had on his conservative ranks in the House. That effort folded, and indeed, as Krone had been predicting, it seemed that the economy was headed for a brief-but-significant jolt of higher taxes.

Many Democrats figured that once the cliff had been jumped, all the leverage would be in their hands and they could extract even deeper concessions from Republicans, particularly on across-the-board spending cuts that they wanted to nix.

Reid and McConnell engaged in some brief talks — talks that included a key mistake by Democrats: They made an offer on the tax levels, and Republicans actually accepted it. There were other key issues to resolve, but once that central issue was settled, the momentum headed toward resolution.

At that point, McConnell called Biden and famously asked: “Does anyone down there know how to make a deal?”

Reid, Schumer and other leaders and their advisers then waited to see the final details, furious that the deal was being made. Democrats leaked stories to The Post, Politico and other outlets about how at one point Reid took an offer that Obama was considering making to McConnell and threw it into the fireplace in his office on the second floor of the Capitol as others watched.

On Tuesday, after Democrats got stomped, the man they feared the most, Mitch McConnell, had the biggest smile of all.

“Friends, this experiment in Big Government has lasted long enough. It’s time to move in a new direction,” he said in claiming victory.